I've replaced the parking brake shoes on both my 123 & 124 cars. They're pretty much identical in both cases. While not my favorite job, it is pretty easy. A good mechanic could do it 1 hour, 1.5 tops. I've done it in 2, working in my home garage, and without any specialized tools for installing the return springs. (Stretching out the return springs is the ^#(&* hard part!)
In both cases I paid ~$30 for the kit with brake shoes & hardware. Figure on 100% markup at a dealer or mechanic.
If the PO never, ever used the parking brake - quite common in North America - you may also be looking at new cables. This will add significantly to the cost, both for parts & labor.